Method and device for controlling a drive unit of a vehicle

ABSTRACT

A method and arrangement for controlling a drive unit of a vehicle are suggested. A desired torque value or a desired power value is formed on the basis of the driver command which serves to control the drive unit. A maximum permissible torque or a maximum permissible power is determined and the desired value is limited to the maximum permissible value when the desired value exceeds the maximum permissible value.

FIELD OF THE INVENTION

The invention relates to a method and an arrangement for controlling adrive unit of a vehicle.

BACKGROUND OF THE INVENTION

Such a method and such an arrangement are known from U.S. Pat. No.5,692,472. There, to control the drive unit, the torque or the power ofthe drive unit is adjusted electrically at least in dependence on theposition of an operator-controlled element actuated by the driver. Amaximum permissible torque or a maximum permissible power is determinedon the basis of the position of the operator-controlled element as wellas at least on the engine rpm. The maximum permissible torque or themaximum permissible power of the drive unit should not exceed the torqueor the power during the actual operating state. The actually adjustedtorque or the actually adjusted power of the drive unit is determinedfrom operating variables such as engine rpm and the inducted air mass.This actual adjusted torque or power is compared to the maximumpermissible value and a fault reaction is initiated when the computedtorque or the computed power exceeds the maximum permissible torque orthe maximum permissible power. With this monitoring measure, theoperating reliability of the drive unit is ensured because a torquegeneration of the drive unit, which is increased compared to the drivercommand, can be prevented in a reliable manner. The response of theshown monitoring is only wanted in the actual case of a fault. Inaddition, operating situations are conceivable (for example, intransition states), in which the monitoring responds to tightly pregiventolerances without a fault being present. Such a behavior is not wanted.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide measures whichavoid an unwanted response of the described monitoring.

A control system for an internal combustion engine on the basis of atorque orientated functional architecture is known from U.S. Pat. No.6,098,592. Here, a drive desired torque is formed from the position ofthe operator-controlled element, which is actuated by the driver, whileconsidering at least the engine rpm. This driver desired torque islogically coupled to external and internal torque requirements in thecontext of coordinators for the adjustment of charge and forinterventions (for example, ignition angle) which are synchronous withthe crankshaft. The resulting desired torques are then, for example,converted into desired ignition angle and desired throttle flapposition. Such an engine control system is shown in FIGS. 1 and 2.

It is ensured that the monitoring on the basis of computed and maximumpermissible torque or power only responds and a fault reaction isinitiated when an actual fault is present via the limiting of at leastone desired value for a torque of the drive unit to the maximumpermissible torque (or via a corresponding measure when the enginecontrol computes engine power values in lieu of torque values). In thisway, the driving comfort and the availability of the drive unit areconsiderably increased. It is especially advantageous that thetolerances for the monitoring of the drive unit on the basis of computedand maximum permissible torque or power can be pregiven very tightly sothat, for an actual fault condition in the region of the engine control,this fault condition can be recognized very quickly and countermeasuresinitiated very rapidly.

In addition, it is of special advantage that the torque desired valuesfor the charge path as well as for the rapid intervention path viainjection suppression, the influencing of the fuel metering and/or ofthe ignition angle are limited to the maximum permissible torque for anengine control system having a torque-orientated functionalarchitecture. In this way, in transition situations and in specialsituations, the maximum permissible torque cannot be exceeded andtherefore a response of the torque monitoring is effectively avoided.The same applies for a power-orientated functional architecture.

It is especially advantageous that a hysteresis between switching on thelimitation and switching off the limitation is provided, preferably forthe rapid intervention quantities.

In an advantageous manner, the influence of the engine drag torquecontrol (MSR) is considered. When the drag torque control is active, thelimiting is disabled because the engine drag torque control can increasethe power. In this way, the engine drag torque function is notnegatively affected. It is especially advantageous that it operates onlyin the rapid path and the MSR can increase the torque for a short time.

For an intervention wherein the ignition angle can be switched off, itis especially advantageous to make triggering the limiting dependentupon the torque to be adjusted via the ignition angle; whereas, theswitchoff of the limiting is pregiven in dependence, inter alia, on thetorque for the fuel metering which is computed on the basis of theaccelerator pedal position. For a switched-off ignition angleintervention, the desired torque for the ignition angle is orientated onthe torque without intervention on the base torque adjusted frompreprogrammed characteristic fields. For this reason, a limiting of theactual torque to the base value is achieved. This contributes in anadvantageous manner to the operational reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in greater detail with respect tothe embodiments shown in the drawings. Here, FIG. 1 shows an overviewblock circuit diagram of a control arrangement for an internalcombustion engine; whereas, in FIG. 2, an overview block circuit diagramof a torque-orientated functional architecture of a control system for adrive unit is shown. FIG. 3 shows a block circuit diagram for thedetermination of the maximum permissible torque as well as of themonitoring measures based thereupon. In FIG. 4, the limiting of thedesired torque value for the charge path is shown in dependence upon themaximum permissible torque; whereas, in FIGS. 5 and 6, two embodimentsfor limiting the desired torque to the maximum permissible torque in therapid intervention path are shown.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1, a control arrangement for a multi-cylinder internalcombustion engine 10 is shown. The control arrangement includes anelectronic control apparatus 12 which comprises at least onemicrocomputer 14, an input unit 16 and an output unit 18. Input unit 16,output unit 18, and microcomputer 14 are connected to each other via acommunication bus 20 for the mutual exchange of data. The input lines22, 24, 28 and 30 lead to the input unit 16. The line 22 originates froma measuring unit 32 for detecting the accelerator pedal position β. Theline 24 originates from a measuring device 34 for detecting the enginerpm nmot. The line 28 originates at a measuring device 38 for detectingthe supplied air mass hfm and the line 30 originates from at least onefurther control apparatus 40 such as a control apparatus for the driveslip control ASR, for the transmission control GS and/or for the enginedrag torque control MSR. For detecting the air mass, and depending uponthe embodiment, air mass sensors, air quantity sensors or pressuresensors for detecting the intake manifold pressure or the combustionchamber pressure are provided. In addition to the operating quantityshown, the control unit detects additional quantities which areessential for engine control, such as the engine temperature, roadspeed, et cetera. An output line 42 is connected to the output unit 18.This output line 42 leads to an electrically actuable throttle flap 44which is mounted in the air intake system 46 of the engine. Furthermore,output lines 48, 50, 52, 54, et cetera are shown which are connected toadjusting devices for the fuel metering into the cylinders of the engine10 or are for adjusting the ignition angle in each cylinder.

In FIG. 2, the basic elements of a torque-orientated functionalarchitecture of an internal combustion engine control are shown withrespect to a block circuit diagram. The elements, which are shown in theblock circuit diagram, are parts of the program of the microcomputer ina preferred realization. The blocks represent special program partshaving tables, characteristic lines, characteristic fields and/orcomputation steps.

The input lines 22, 24 and 28 lead to an element 100 for determining thedriver command torque miped. This torque is conducted via a line 102 toelements 104 and 106. The line 30 leads to each of elements 104 and 106.The elements 104 and 106 serve for selecting the desired torque valuesmildes and mides, which are pregiven for the engine control, inaccordance with the supplied desired torque values of the driver commandas well as external interventions miext (for example, ASR, GS, MSR) andinternal interventions miint (for example, rpm limiting, road speedlimiting). The selected desired values are supplied via line 108 tocomputing unit 112 and via line 110 to computing unit 114. The computingunit 112 computes the correction of the ignition angle and/or theinjection suppression and/or the influence of the mixture composition inaccordance with at least engine rpm and air mass (actual fresh gascharge). In the same manner, the computing unit 114 computes the charge,which is adjusted by driving the throttle flap via the line 42, from thesupplied desired value in accordance with at least engine rpm and airmass (actual fresh gas charge). In a preferred embodiment, the computingelements 112 and 114 are connected via the line 116 for the exchange ofdata.

With the procedure shown in FIG. 2, the various interventions on thetorque of the engine (intervention of an ASR, an MSR, a transmissioncontrol, from the driver, et cetera) are coordinated by an adjustment ofthe charge (slow intervention) via a throttle flap in the air intakepipe and/or by adjusting the fuel metering and the ignition angle (morerapid intervention).

The control system, which is shown in FIG. 1, computes power quantitiesof the engine from its input quantities so that a fault in the region ofthe computation can lead to excessive drive power of the engine andtherefore to a dangerous driving situation. For this reason, andaccording to FIG. 3, it is provided to check the correctness of thecomputations supplied for the power control. This takes place inaccordance with the initially-mentioned state of the art in that amaximum permissible torque mizul is determined and compared to acomputed actual torque miact of the engine and, when the maximumpermissible torque is exceeded by the actual torque, fault reactions areexecuted which are, for example, a switchoff of the fuel metering SKA.

The procedure, which is selected to determine the maximum permissibletorque and to monitor the torque is shown in a preferred embodiment inFIG. 3. Here too, as in the FIGS. that follow, the block circuit diagramis selected for the reasons of clarity and overview. The mentionedfunctions are realized in the preferred embodiment as programs of themicrocomputer of the control unit controlling the engine. The maximumpermissible torque mizul is read out in at least one characteristicfield 200 on the basis of the input quantities accelerator pedalposition β and engine rpm nmot. In the preferred embodiment, this takesplace on the basis of the predetermined characteristic field. In thecharacteristic field, the maximum torque requirement of the pedal, whichis permissible at a specific rpm, is stored while consideringtorque-increasing functions such as, for example, the idle control. Thevalue, which is read out from the characteristic field, is filtered viaa lowpass filter (not shown) as shown in the initially mentioned stateof the art. The lowpass filter is only active for a negative slope ofthe value coming from the characteristic field.

In another advantageous embodiment, two characteristic fields areprovided dependent upon engine rpm and accelerator pedal position. Themaximum permissible torque is here formed as the sum of the twocharacteristic fields. In one characteristic field, the start and theidle control for rpms below the desired rpm are considered which rpmsincrease the maximum permissible torque. The filtering then takes placeonly for the values of the other characteristic field.

The permissible torque mizul, which is determined in this manner, issupplied to a maximum value selector MAX, wherein it is compared to apregiven fixed value mdimax. This value defines the maximum adjustabletorque. The value mdimax is outputted when the road speed controller isactive (FGR_in). For a deactivated road speed controller, the value 0 isapplied to the corresponding input of the maximum value selector. Thelarger of the supplied torque values (mizul, mdimax or 0) is furtherprocessed as the maximum permissible torque mizul. In this way, it isensured that in road speed control operation and when the acceleratorpedal is released, the maximum permissible torque is not too low anddoes not respond to the fault reaction. The maximum permissible torquemizul is made available (output A) to limit the desired torques as willbe described in FIGS. 4 to 6.

An actual torque results from the maximum permissible desired torque. Ina higher-order monitoring level, the actual torque miact is compared toa permissible torque mimax.

This permissible torque is computed in a similar manner as thepermissible desired torque. An example for such a computation isdescribed in the state of the art initially mentioned herein. Thecomputation is executed in computation step 203. The maximum permissibletorque mimax is, as a rule, greater than the permissible torque mizulwhich is used for limiting. A filtering (in 203) should here considerthe intake pipe time constant, position controller deceleration andtorque-increasing functions (for example, dashpot).

If the actual torque miact exceeds the maximum permissible torque mimax(comparator 204), the switchoff of the fuel metering SKA is triggeredafter a delay time (if required) in order to control the detected faultcase. The actual torque miact is computed in 205 at least on the basisof engine rpm nmot and air mass hfm.

In FIG. 4, the limiting of the desired torque value mildes is shown forthe charge path. In the preferred embodiment, this is carried out incoordinator 104 in which the pedal torque miped, which is derived fromthe driver, is compared in a maximum value selector MAX totorque-increasing external and/or internal interventions such as, forexample, an MSR. The largest value is then compared in a minimum valueselector MIN to torque-reducing external and/or internal interventionssuch as ASR, an rpm limiting and a road speed limiting. The maximumpermissible torque mizul is supplied additionally to this minimum valueselector MIN. In each case, the smallest of these desired torques isselected and outputted as desired torque value mides for the chargepath. If all torque demands exceed the maximum permissible torque, thenthis maximum permissible torque is outputted as the desired torque valuefor the charge path. In this way, the desired torque value mildes forthe charge path is limited to the maximum permissible torque mizul.

A limiting is also executed in the intervention path synchronous withthe crankshaft. FIG. 5 shows a first embodiment of the coordinator 106.First, and in a manner comparable to FIG. 4, the coordinator 106 forms adesired torque midesv for the intervention path synchronous with thecrankshaft in a maximum value selector and/or a minimum value selectorMIN, MAX from the pedal torque miped, the external desired torque miextand/or the external desired torque miint. The determined desired torquemidesv is then compared in a comparator 300 to the permissible torquemizul. If the computed desired torque midesv exceeds the maximumpermissible torque mizul, the comparator 300 outputs a logic 1-signalwhich is supplied to an AND gate 302. Furthermore, the desired torquemidesv is supplied to a comparator 304 in which it is compared to avalue (mizul-mihyst), which is formed from the maximum permissibletorque mizul. This value defines the maximum permissible torque reducedby a pregiven hysteresis torque mihyst. If the desired torque valuedrops below this value, then a logic 1-signal is outputted to an OR gate306. The output of the OR gate is supplied to the reset input of an RSflipflop 308 and to the negative input of the AND gate 302. A signalB_msr is also supplied to the OR gate 306 and this signal has a positivesignal level when an engine drag torque control is active. The output ofthe AND gate 302 is supplied to the set input S of the RS flipflop 308.The output signal Q of the flipflop 308 leads to a switching element 310which goes into a switching state with a corresponding signal. In theswitching state, the maximum permissible torque mizul is transmittedfurther as the desired torque mides for the rapid intervention path inlieu of the desired torque value misolv.

If the desired torque misolv exceeds the maximum permissible torquemizul when the engine drag torque control (B_msr=0) is not active, thenthe flipflop 308 is set via the AND gate 302. The output Q goes to a“high” level so that the switch 310 switches over the position shown inphantom outline. If the desired torque value drops below the maximumpermissible torque reduced by the hysteresis value, then a signal isformed by the comparator 304 which resets the flipflop 308. At the sametime, a level change to logic 0 at the set input takes place via the ANDgate 302. This has the consequence that the switch 310 is again switchedover into the solid-line position via the output Q of the flipflop 308.If the engine drag torque control is active (B_(—msr=)1), the resetinput of the flipflop 308 is set to logic 1-level via the OR gate 306;whereas, the level 0 is supplied continuously to the set input. In thisway, the switch 310 is held in its solid-line position so that, foractive engine drag torque control, the desired torque mides can beraised, if required, above the maximum permissible torque mizul.

In a preferred embodiment shown in FIG. 6, a desired torque value mideszis derived for the ignition angle intervention from the desired torquevalue midesv determined by the minimal selection/maximum selectionMINMAX. Here, especially additive corrective components Δ mi of an idlecontrol LLR and an antibucking function ARF are considered. The ignitionangle desired value is configured so that it can be switched (switch400) so that, in specific operating situations, not the desired torquevalue misolv, but a base torque value mibas is used as the basis for thedesired torque value formation for the ignition angle. The base torquemibas corresponds to the torque which would be assumed, in the actualoperating state, by the engine while considering the preprogrammedignition angle setting and the λ setting. The base torque is formed onthe basis of the air mass hfm, the engine rpm nmot as well as the torqueeffective lines of the base ignition angle and the λ base setting. Theprocedure for limiting both desired torque values corresponds to theprocedure shown in FIG. 5. The desired torque value for the ignitionangle intervention is supplied to the comparator 300 and is therebyapplied for deciding whether there should be limiting. In contrastthereto, the desired torque value misolv for the fuel path is suppliedto the comparator 304 which decides as to the interruption of thelimiting. If the limiting criterion or breakoff criterion is satisfied,then the switching element 310 is correspondingly actuated. Forlimiting, both desired torque values mides and midesz are replaced bythe maximum permissible torque mizul.

The invention was described for a torque orientated function structure.A corresponding procedure is used for an engine control on the basis ofpower values. Here, the above-mentioned torque value is replaced by thecorresponding power quantity which relates to the torque via the rpm.

What is claimed is:
 1. A method for controlling a drive unit of avehicle, the method comprising the steps of: at least on the basis of adriver command, forming at least a desired value for the torque of thedrive unit or at least a desired value for the power of the drive unit;adjusting at least the one desired value by controlling the drive unit;determining a maximum permissible torque or a maximum permissible powerat least on the basis of the driver command; limiting the at least onedesired value to said maximum permissible torque or said maximumpermissible power when the desired value thereof exceeds the maximumpermissible value to provide a limited at least one desired value; and,controlling the drive unit according to said limited at least onedesired value.
 2. The method of claim 1, wherein the at least onedesired value is a desired torque value or a desired power value whichis adjusted by influencing the charge of an internal combustion engine.3. The method of claim 2, wherein the desired value for the charge pathis limited to the maximum permissible value in that a minimum valueselection is carried out between the quantities, which form the desiredvalue, and the maximum permissible value.
 4. The method of claim 1,wherein the at least one desired value is a desired torque value or adesired power value for crankshaft synchronous interventions such asfuel metering and ignition angle.
 5. The method of claim 4, wherein thedesired value is compared to the maximum permissible value, and asdesired value, the maximum permissible value is transmitted further whenthe desired value exceeds the maximum permissible value.
 6. The methodof claim 5, wherein the limiting is switched off when the desired valuedrops below a pregiven value which is derived from the maximumpermissible value.
 7. The method of claim 6, wherein the limiting isdeactivated when an engine drag torque control is active.
 8. The methodof claim 7, wherein a desired value for the fuel metering is determinedand, while considering additional interventions, a desired value for theignition angle path is determined; the limiting is triggered when thedesired value for the ignition angle exceeds the maximum permissiblevalue and the limiting is disabled when the desired value for the fuelmetering drops below a pregiven value.
 9. The method of claim 1, whereina further maximum permissible torque or a maximum permissible power iscompared to a computed actual torque of the drive unit or of a computedactual power and a fault reaction is initiated when the actual valueexceeds the maximum permissible value.
 10. An arrangement forcontrolling a drive unit of a vehicle, the arrangement comprising: meansfor determining at least one desired torque value of the drive unit orat least one desired value for the power of the drive unit forcontrolling the drive unit at least in dependence upon a driver command;means determining a maximum permissible torque value or a maximumpermissible power value at least in dependence upon the driver command;means for limiting the at least one desired value to the maximumpermissible value when the desired value exceeds the maximum permissiblevalue to provide a limited at least one desired value; and, means forcontrolling the torque or the power of said drive unit according to saidlimited at least one desired value.